This invention relates to a method for the continuous assembly and the batch molding of transistor packages and more particularly to the use of a lead frame and a transistor bearing metal ribbon in the process.
For over a decade, transistors have been manufactured by assembling transistor chips to lead wire sets employing a chip bearing metal ribbon. The leads in each set are held relative to each other by means of a temporary header and the header held lead sets are in turn fed and guided to a work station by means of rails and other external mechanical means. A major limitation to the speed of assembly of transistors to lead sets in this system is the limited speed with which it is possible to successively feed and accurately register the separate lead sets in the work stations. Furthermore, the resin encapsulation of the individual transistor connected to a lead set is normally accomplished by casting with an epoxy resin, which is slow and requires a considerable amount of operator attention. Lead sets are not readily molded because of their lack of a disciplined geometry.
In other conventional methods for making transistor packages, a short lead frame strip is employed on which typically from 10 to 50 transistor chips are mounted. These strips of uniform geometry are then inserted into a multi-cavity mold and the transistors are individually molded in a protective resin encapsulant by a low cost standard transfer or injection molding step. It is believed that all users of lead frames for component assembly only assemble to such short lead frame strips, and that continuous assembly to long or continuous lead frames is unknown.
It is therefore an object of this invention to provide a method for the continuous assembly of transistors to a long lead frame.
It is a further object of this invention to provide a low cost method for assembly of transistor chips to a lead frame that is compatible with a subsequent low cost encapsulation step.
It is yet a further object of this invention to provide a method for the mass production of a lower cost transistor package.